The present invention relates to a fluorescent luminous tube useful as a write element such as an optical print head, and to a method of manufacturing the same.
FIG. 5 is a cross-sectional view illustrating a fluorescent luminous tube acting as a write element for an optical print head, proposed by the present inventor. FIG. 6 is a perspective view partially illustrating the configuration inside the housing in FIG. 5.
The fluorescent luminous tube has a housing formed of a box-like container 2 (with an open lower end) for hermetically sealing the upper surface of a translucent insulating substrate 1. Anodes and bars of a grid are two-dimensionally disposed on the upper surface of the substrate 1 at intervals. Each anode is isolated from each grid bar.
A number of strip-shaped anode conductors 3 (led out from the container and each acting as an anode wire being a power feed terminal) are formed on an inner surface of the substrate 1. Anode conductors 3 are arranged in parallel and at predetermined intervals and are arranged in the direction (in the secondary scanning direction of an optical print head) perpendicular to the longitudinal direction thereof (to the primary scanning direction of an optical print head). A square opening 4, through which the substrate 1 is exposed, is formed at the front end of each anode conductor 3. A fluorescent substance layer 5 is formed in the opening 4. As shown in FIG. 6, two groups of anode conductors 3 placed in the primary direction are arranged in the secondary scanning direction at predetermined intervals. The two groups of anode conductors are shifted from each other in the primary scanning direction by one-half the pitch at which luminous dots are arranged. Two columns of a large number of square luminous dots (fluorescent substance dots) defined in the openings 4, which are arranged at predetermined intervals in the primary scanning direction, are observed from the outside of the substrate 1. In other words, the luminous dots are arranged in zigzag form. The respective anode conductors 3 are led out from the container and are connected to the drive element (IC) 7 mounted on the drive circuit substrate 6.
On the inner surface of the substrate 1, the bars of the flat grid 8 are placed between anode conductors 3 and so as to spaced apart from the anode conductors 3. The bars of the grid 8 are integrally formed electrically and are placed in the gaps between the plural stripe-shaped anode conductors 3 arranged in parallel. The grid 8 has a comb-like structure.
Cathodes 9 each acting as an electron source, as shown in FIG. 5, are disposed inside the container. Shield electrodes 10 are placed inside the container in such a way that a reactive current does not flow to various conductors formed on the substrate 1. A NESA film 11 is formed on the inner surface of the rear plate of the container 2, confronting the substrate 1.
In the above-mentioned structure, electrons emitted from the cathode 9 collide with the fluorescent substance layer 5, thus emitting light. The light emission of the fluorescent substance layer 5 is observed, as a predetermined dot defined by the opening 4, from the outer surface of the substrate 1. When an optical write object and a fluorescent print head are relatively moved in the secondary direction, light beams emitted from two columns of luminous dots arranged in zigzag form can form a single line continuing in the primary scanning direction on the optical write object. In order to draw an image on an optical write object, the fluorescent print head is first suitably driven in accordance with drive information created from image information. Then, the fluorescent print head and an optical write object (not shown) formed of a silver salt paste are relatively moved in synchronous with the drive operation.
However, in conventional fluorescent luminous tube, part of light beams radiated toward the rear surface (the NESA film 11) from the fluorescent substance layers 5 backs to the front surface (the observer side) due to irregular reflection. The backed light leaks to the front side through the gap between the anode conductor 3 and the bar of the grid 8, thus resulting in a low contrast.
Moreover, because the fluorescent substance layer 5 is formed using the photolithography, the openings 4 in anode conductors 3 have to be aligned with the photo mask with high precision. Alignment with low precision results in the fluorescent substance coated at the position displaced from the anode conductor 3 on the substrate 1. That fluorescent substance light-emits in drive operation and is observed as a minute luminous point. Such a defective (NG) element cannot be used as a write element. For that reason, the realizable resolution of the conventional fluorescent luminous tube is limited to 300 dpi.
The present invention is made to solve the above-mentioned problems.
An object of the invention is to provide a fluorescent luminous tube wherein the light leaking from the gap between an anode conductor and bars of a grid is blocked so as to obtain a high contrast. Another object of the present invention is to provide a method of manufacturing a fluorescent luminous tube with high resolution, without accurately aligning anode conductors with a mask in a fluorescent substance layer fabrication step.
The objective of the present invention is achieved by a fluorescent luminous tube comprising anode conductors (3) and bars of a grid (8), each being arranged over an inner surface of a translucent substrate (1) and spaced apart from one another, the anode conductors each having an opening (4) which exposes the substrate; a fluorescent substance layer (5) formed in the opening; a housing (2) for sealing the inner surface of the substrate; an electron source (cathode 9) disposed inside the housing; and a lightproof insulating layer (12) formed in the gap between each anode conductor and each bar of the grid.
According to another aspect of the present invention, a fluorescent luminous tube comprises a translucent substrate (1); a plurality of anode conductors (3) arranged over an inner surface of the substrate at predetermined intervals, each of the anode conductors having an opening which exposes the substrate; a fluorescent substance layer (5) formed in the opening; a grid (8) arranged over the inner surface of the substrate, bars of the grid being disposed between the anode conductors and spaced apart from the anode conductors; a housing (2) for sealing the inner surface of the substrate; and an electron source (cathode 9) disposed inside the housing. This structure further includes a plurality of luminous dots where luminous substance layers each defined by the opening are arranged at the predetermined intervals, viewed from the outer surface of the substrate. Moreover, a lightproof insulating layer (12) is formed on the inner surface of the substrate so as to bury the gap between each anode conductor and each bar of the grid.
In the fluorescent luminous tube, the thickness of the lightproof insulating layer (12) does not exceed the thickness of a fluorescent substance layer (5).
In the fluorescent luminous tube, light emission of the fluorescent substance layer (5), which results from impingement of electrons emitted from the electron source (cathode 9), is observed from the side of the substrate via said opening (4) and the substrate (1), or light emission of each luminous dot, which results from impingement of electrons emitted from the electron source, is illuminated out from the substrate via the opening and the substrate.
Moreover, in a method of manufacturing a fluorescent luminous tube, according to the present invention, first, a plurality of anode conductors is formed on an inner surface of a translucent substrate (1) at intervals, each of the plurality of anode conductors (3) having an opening (4) which exposes the substrate. Next, a photosensitive resist (18) is coated all over the inner surface of the substrate. The photosensitive resist is light exposed via a mask, the mask being disposed so as to confront the inner surface of the substrate. Thus, a lightproof film is formed only the inside of the opening. Next, a photosensitive lightproof fluorescent insulating material (photosensitive black matrix 20) is coated all over the inner surface of the substrate. The entire outer surface of the substrate is light exposed. The lightproof film in the opening is removed while a lightproof insulating film (12) is formed only on the substrate between the anode conductors. Next, a photosensitive fluorescent substance (fluorescent substance paste 21) is coated in the inner surface of the substrate to at least the opening and the substrate is light exposed. Then, a fluorescent substance layer (5) is formed.